The present invention relates generally to sealing means for downhole tools and, in an embodiment described herein, more particularly provides a seal structure for a downhole tool.
It is well known that significant problems are typically encountered when an attempt is made to sealingly engage a seal bore in a downhole tool in an abrasive environment. Such an abrasive environment may exist, for example, in a fracturing or gravel packing job. These problems are multiplied when such sealing engagement must be performed multiple times downhole.
FIGS. 1A and B illustrate a representative example of such a situation. A prior art seal structure 10 is disposed externally on a mandrel 12 of a downhole tool. The seal structure 10 includes a seal support ring 14 and two seals 16 disposed in open-sided grooves 18 formed externally on the ring. The seals 16 are bonded to the ring 14 in the grooves 18.
It is desired to have the seal structure lo enter a seal bore 20 and effect a pressure bearing seal between the mandrel 12 and the seal bore. Unfortunately, sand 22, or another abrasive material, such as synthetic proppant, etc., has accumulated between the mandrel 12 and the seal bore 20. When the seal structure 10 enters the seal bore 20, the sand 22 is compressed between the seals 16 and the seal bore, as may be seen in FIG. 1B.
Compression of the sand 22 between the seals 16 and the seal bore 20 may not cause immediate failure of the seals. However, with repeated cycles of the seal structure 10 entering and withdrawing from the seal bore 20, the seals will eventually deteriorate.
This problem appears to be exacerbated where a relatively large degree of compression is experienced in the seals 16 when they enter the seal bore 20. Note that the seals 16 fill the grooves 18 and so, when the seals enter the smaller diameter seal bore 20, they are compressed inwardly against walls of the grooves, as well as being significantly compressed against the seal bore and the sand 22 between the seals and the seal bore. An improved seal structure should provide space for the seals to deflect inwardly when a seal bore is entered, so that compression of the seals against the seal bore is reduced.
Another problem experienced in these situations is high xe2x80x9cstabbingxe2x80x9d force. That is, the force which must be exerted against the seal structure 10 to urge it into the seal bore 20. In general, high stabbing forces are to be avoided, since they are known to cause seal damage, they may cause operational problems, etc. An improved seal structure should reduce the stabbing force needed for the seal structure to enter a seal bore.
In carrying out the principles of the present invention, in accordance with an embodiment thereof, a seal structure is provided which solves the above problems in the art.
In one aspect of the invention, a seal structure for a downhole tool is provided which includes a seal support ring and a seal. The seal support ring has at least one annular groove formed thereon. The seal is disposed at least partially in the groove, the seal is bonded to the ring, and the seal has an annular recess formed thereon.
The recess may have a variety of cross-sectional shapes. In addition, the recess may be positioned in various portions of the seal body. Furthermore, there may be multiple seals disposed in multiple respective grooves on the ring.
In another aspect of the invention, another seal structure for a downhole tool is provided. The seal structure includes a seal support ring having at least one annular groove formed thereon and a longitudinal axis. A seal is disposed at least partially in the groove, and the seal is bonded to the ring. An annular recess is positioned longitudinally between opposing side walls of the groove.
Again, the recess may have a variety of cross-sectional shapes, the recess may be positioned in various portions of the seal body, and there may be multiple seals disposed in multiple respective grooves on the ring. In addition, the recess may be formed in a body of the seal.
In yet another aspect of the invention, another seal structure for a downhole tool is provided which includes a seal support ring, at least four seals and at least two recesses. The seal support ring has first, second, third and fourth spaced apart annular grooves formed on a surface thereof. First, second, third and fourth seals are bonded in respective ones of the first, second, third and fourth grooves, with the second and third seals being disposed between the first and fourth seals. A first annular recess is positioned between opposing side walls of the second groove, and a second recess is positioned between opposing side walls of the third groove.
These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings.